Magnet Wire Faq

Magnet Wire FAQ

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Electrical Insulating Varnish for Magnet Wire
Magnet Wire FAQ


General Information

What is magnet wire?

Magnet wire, or enamelled wire, is a copper or aluminium wire coated with a very thin layer of insulation.

Applications: What is it used for?

Magnet wire is used in the construction of transformers, inductors, motors, speakers, hard disk head actuators, potentiometers, electromagnets, and other applications which require tight coils of wire.

What is the difference between copper and aluminum magnet wire?

Aluminum has lower conductivity than copper, so aluminum wire needs a larger cross section to compensate. For this reason, copper wire is more energy efficient.

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Insulation: What is it and what does it do?

The insulation can be either a thin varnish, or enamel; a yarn made out of polyester or fiberglass; or both.

If the wire were bare, the turns of the wire would not be able to not touch each other, as they would short out, while insulated wire can be wound so that the wires are touching. For a wire that will have hundreds or thousands of turns, insulation is absolutely necessary.

Insulation Types: What are some common types used in magnet wire?

Different insulation types for magnet wires that will have different thermal capacity, diameter (which can be measured in millimeters or inches), AWG wire size and application.

Here are some common types of insulation and their specifications:

Insulation Type Thermal Class Diameter (mm) Diameter (in.) AWG Wire
Size Range
Polyurethane 120°C, 130°C, or 155°C 0.08 to 1.00 0.0031 to 0.0394 20-18 Transformers, meters, and communication devices.
Polyester 155°C 0.08 to 1.6 0.031 to 0.063 20-14 Motors in household appliances.
Polyester-imide 180°C 0.1 to 1.00 0.0039 to 0.0394 38-18 High powered motors.
Polyamideimide 220°C 0.1 to 1.6 0.0394 to 0.063 38-14 Small motors and transformers.
Self-bonding polyurethane 130°C 0.08 to 1.2 0.0031 to 0.0472 20-16 Communication apparatus and small motors.
Self-bonding Polyester-imide 180°C 0.1 to 0.8

0.0039 to 0.031

38-20 Used in magnetic coils and deflection york application.
Polyurethane overcoated with polyamide 130°C or 155°C 0.08 to 1.6 0.0031 to 0.063 20-14 Small motors and transformers.
Polyester overcoated with polyamide 155°C or 180°C 0.1 to 1.6 0.0039 to 0.063 38-14 Used in small motors.
Polyester-imide overcoated with polyamide-imide 200°C 0.1 to 1.6 0.039 to 0.063 38-14 Microwave oven transformers and air-conditioning motors.

What is Insulation Thickness?

Insulation thickness, or build, is the measurement of enamel that has been added to the circumference of the wire. It can be determined by taking the total diameter of the wire and the enamel together, and then subtracting the diameter of just the wire from the total diameter.

Insulation build can be single, heavy, triple or quadruple, with single and heavy being the most common. Single insulation thickness for a 24 gauge wire can be 0.0010 inches, and 0.0019 inches for a heavy build. For 40 gauge wire, single build can be 0.0002 inches, and 0.0006 inches for heavy build.

Larger insulation builds are used to make the wire stronger or to offer more protection.

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What is American Wire Gauge (AWG)?

American wire gauge (AWG) is used in the U.S. and Canada to represent the diameter of round, solid wire.

How does the diameter of the wire affect the gauge?

As magnet wire diameters decrease, the AWG number increases. For example, a wire with a diameter of 4.621 millimeters will have an AWG size of 5, while a wire with a diameter that measures 0.255 millimeters will have an AWG size of 30.

There are 44 standard wire sizes: 0000-40. Any wire size beyond those gauges will be so small they will need to be measured in ohms.

How do I determine the weight of my wire?

Like the diameter, wire weight is based on AWG standards. The weights of each gauge are standardized. As the gauge becomes greater, the weight of the wire will decrease.

The largest wire weight is 640.5005 lbs per 1000 feet, with a gauge of 0000. For a 40 gauge wire, the weight is 0.0299 lbs per 1000 feet.

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What temperature rating/thermal class?

The thermal class, or temperature rating, is the maximum temperature that the magnet wire can be exposed to. Thermal class is measured in degree celsius. 130°, 155°, 180° and 200° are some common temperatures found in different types of insulation. The maximum thermal class is 250° celsius.

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Wire Shape and Appearance

What is the difference between round and square magnet wire?

Square magnet wire will have less space between the wires when formed in a coil. For this reason, square wire is used in confined spaces.

AWG ratings only apply to round wire.

Solid vs. Stranded Wire

Solid magnet wire is a single strand of insulated wire. They do not bend easily, and are used in applications where they are not frequently moved.

Stranded magnet wire are multiple wires braided together. These types of wires are flexible and easy to install.

What does the color of the magnet wire mean?

Magnet wire can come in a variety of colors, including red, green and amber. This is purely aesthetic, though, and will have no bearing on how the wire will function or its insulation properties.

If a certain wire color is required, some manufacturers will provide customers with a wire in that color.

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What is bondable magnet wire?

Bondable magnet wire has an extra adhesive film on top of the usual insulation. When the adhesive is activated, it will bond the turn to turn windings into a self-supporting coil.

What is solvent bondable magnet wire?

This kind of bond coat will be applied either while the wire is winding, or the coiled wire will be dipped in the solvent after it has already been winded. The coil then needs to be heated up again to complete the bonding and to dry off any additional solvent.

Bondable magnet wire may not always be able to withstand the temperature rating of some insulations.

What is oven bonding?

After the wire is winded, the coil is put into an oven that will allow the bond coat to bond the wire together. Oven bonding can take 10 to 30 minutes, depending on the size of the coiled wire.

What is resistance bonding?

Resistance bonding is very similar to oven heating, but in this case an electric current is used to heat up the coil. There is no uniform heating time for resistance bonding; voltage and time are dependent on wire size and coil design. This method is typically used for wire sizes 34 gauge or higher.

Does magnet wire have a shelf life?

As long as magnet wire shelf life is carefully stored it should be usable for years.

Bondable wire should not be stored at temperatures exceeding 100°F.

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